In a portable telephone set, when charging a rechargeable battery mounted in it, the power supplying connector of a charger is connected to an external device connecting connector. In recent years, the housing of the portable telephone set is becoming more compact and thinner than before. Accordingly, the connectors are also becoming compact and thin. The size and thickness of a connector tend to be inversely proportional to the physical strength of the connector. When inserting and pulling out the connectors, the connectors or their peripheral portions may be damaged. In view of this, countermeasures to prevent damages are taken by, e.g., changing the material of the connectors from a conventional plastic material to a metal.
As an example of a portable telephone set of this type, for example, one shown in FIG. 6 is available.
This portable telephone set 1 has, e.g., a foldable housing, and comprises a unit 2, unit 3, and hinge 4, as shown in FIG. 6. The unit 2 comprises a display 5 and receiver 6 on its front surface. The unit 3 comprises a microphone 7 and operation keys 8a and 8b on its front surface, a connector 9 on its end face, and incorporates a controller and rechargeable battery (not shown). The units 2 and 3 are folded through the hinge 4 such that their front surfaces oppose each other.
An AC adapter 10 to charge the rechargeable battery is prepared as an accessory to the portable telephone set 1. The AC adapter 10 is provided with an AC power supply plug 11, cable 12, plug 13, and notice tag 14. When charging, the plug 13 is connected to the connector 9. The notice tag 14 describes notices concerning the attaching/detaching (inserting/pulling-out) operation of the plug 13. The AC adapter 10 supplies power with a charging voltage of 4.2 V/1,000 mA that matches the standard of the rechargeable battery formed of, e.g., a lithium ion battery.
As shown in FIG. 7, the connector 9 of the portable telephone set 1 has an iron metal case 9a. The iron metal case 9a is provided with metal claw catches 9b at predetermined portions. The plug 13 of the AC adapter 10 is provided with iron metal claws 13a and metal claw release hooks 13b. When fitting the connector 9 and plug 13 with each other, the iron metal claws 13a of the plug 13 are fitted with the metal claw catches 9b of the connector 9. Thus, the connector 9 and plug 13 are reliably fitted with each other to ensure electrical characteristics. When pulling out the plug 13 from the connector 9, the user pinches the metal claw release hooks 13b, so that the iron metal claws 13a disengage from the metal claw catches 9b. 
As shown in FIG. 8, the portable telephone set 1 has a power supply unit 20. The power supply unit 20 comprises a charging circuit 21 and battery 22. The portable telephone set 1 is connected to the AC adapter 10 through the plug 13 in FIG. 6. The AC adapter 10 supplies power to the power supply unit 20 of the portable telephone set 1 through a + terminal VCHG and ground terminal GND of the plug 13 and the connector 9 of the portable telephone set 1.
FIG. 9 shows an example of the characteristics of the charging current of the battery 22 in FIG. 8. The axis of ordinate represents a charging current ICHG or battery voltage V, and the axis of abscissa represents a charging time T.
As shown in FIG. 9, during a preliminary charging period T1 immediately after the start of charging, the charging circuit 21 is controlled to preliminarily charge the battery 22. The relationship between a voltage value (battery voltage) e of the battery 22 and the time is monitored to check if there is any abnormality. If the voltage value e satisfies a prescription value and charging of the battery 22 is normal, the charging process shifts to a quick charging period T2. During the quick charging period T2, the charging current ICHG of about 1,000 mA is supplied to the battery 22 to perform constant current driving. The charging voltage is thus quickly raised to near 4.2 V to perform charging. After that, when the voltage value e reaches near the rated value of 4.2 V, the charging process shifts to a trickle charging period T3. During the trickle charging period T3, the charging current ICHG corresponding to the voltage difference between the AC adapter 10 and battery 22 is supplied to the battery 22 to perform constant current driving. As the voltage difference gradually decreases, the charging current also decreases. When the voltage difference disappears at a point F, charging is completed. At this time, the charging current value is zero.
Other than the portable telephone set 1 described above, as a related technique, for example, one described in reference 1 (Japanese Patent Laid-Open No. 2005-045490) is available.
According to the connector structure of the portable terminal device described in reference 1, an electromagnet is attached to a connector main body, and a metal piece to be attracted by the electromagnet is attached to a connector connection port. A switching circuit performs switching between energization and non-energization to the electromagnet on the basis of a control signal output from a portable terminal device main body.